There many methods for displaying contour lines in visualization and GIS software programs. In most cases, representing terrain data with standard contours or hillshading techniques are sufficient. In other cases, you may want a more artistic technique to help emphasize specific features in the data or to make the map more pleasing to the eye. One of these techniques is using the Tanaka method for creating illuminated contours. I recently read an article about how to create illuminated contours in ArcGIS and couldn’t resist trying to replicate the results in Surfer's mapping software.
The Tanaka method applies a northwest light source to a contour map. The contour lines then change in color and width based on their relationship to the light source. Contour lines facing the light source are drawn in white while those in the shadow are drawn in black. The contour lines facing the light source (or facing away from it) are thicker, and the contour lines in the orthogonal direction are thinner. A more detailed explanation of the method can be found online at: http://www.mbmg.mtech.edu/pdf/gis_illum.pdf